A block signal uses colored lights to inform a train engineer of the traffic condition in track blocks ahead. A green light indicates that the block ahead is clear; a red light indicates the next block is occupied. A yellow light can be used to indicate the block after the next block is occupied (proceed at reduced speed.)

The Model Power No. 991 "3-Lited Railroad Signal" is intended for a "G" Scale train layout, but its size is compatible with toy train layouts. It is 8 1/2" high, making it a 1:48 scale model of a 34' high railroad signal. Model Power also offers a similar No. 990, "2-Lited Railroad Signal."

The base, post, and lights fixture are molded plastic. The bracket holding the light fixture is also plastic, and very fragile; exercise caution when changing bulbs. Light hoods are formed brass sheet. The ladder is formed sheet metal.

Light bulbs are mini-screw, 24 volts, 3 watts. Model Power recommends operation at 12 - 18 volts.

The Model Power No. 991 comes with one yellow and three brown wires attached to a slide switch. Since the block signal will be operated automatically as trains move across track blocks, the switch isn't needed; cut it off and extend the wires as required. The yellow wire is the common for all three lights and is usually connected to one side of a 12 - 18 volt accessory transformer. There is one brown wire for each light bulb, connected to the output terminals of a Three-Rail Innovations' Two Relay Controller .

The Two Relay Controller has four features for specifically operating block signals: Off/On, Prototypical, Flashing, and Warning. Click on any of the following for examples.

There are two basic ways to connect a three-light block signal to a controller.

One way is to simply connect the lead for the yellow light of the first block to the Controller output terminal for the red light of the block signal for the second block.

If the previous way cannot be used, then a two-light block Signal 2RC feature is used along with an additional relay in ON/OFF mode. The two-light block signal feature is operated by the isolated rail for the track block following the block signal (operating the top and bottom lights,) and the isolated rail for the second block connected to the input for the additional ON/OFF feature. The relay for the additional ON/OFF feature is connected to the yellow light.

The 2RC relay and power connections needed for a three light block signal are shown in the diagram to right, using a Model Power No. 991 accessory. This accessory comes with one yellow and three brown wires attached to a slide switch. We don't need the switch, so cut it off and extend the wires as required. The yellow wire is the common for all three lights.

The Combining Track Blocks technique can be used to operate the yellow light if there is a train in the second or third track block.

We use the 2RC ON/OFF mode this example, but other features can be used. Some features, with appropriate changes to the input and output connections, will flash the yellow light or reverse its sense (ON when the block is clear). You can implement whatever block signaling scheme you prefer.

Block signal operation does not have to be prototypical. A 991 block signal has three lights and the 2RC can be connected to operate the lights any way you want. It's your railroad, you can make the block signal lights do anything you want.